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Rocky Mountain High: Ecological and Hydrological Effects of Increases in Atmospheric CO2 and Air Temperature
Reference
Baron, J.S., Hartman, M.D., Band, L.E. and Lammers, R.B. 2000. Sensitivity of a high-elevation Rocky Mountain watershed to altered climate and CO2. Water Resources Research 36: 89-99.

What was done
The authors employed a regional hydro-ecological simulation model to evaluate the consequences of a doubling of the air's CO2 concentration and 2 to 4C increases in air temperature on a high-elevation Rocky Mountain watershed.

What was learned
"Both photosynthesis and transpiration were highly responsive to doubled CO2," say the authors. In addition, the positive effects provided by the 4C temperature increase "were additive, so a warmer and carbon-rich environment increased plant growth by 30%." The authors note their results suggest that "forests will expand at the expense of tundra in a warmer, wetter, and enriched CO2 world," and that observed increases in tree height and density in recent decades illustrate "the rapidity with which vegetation can respond to climate change."

With respect to water resources, even though the doubled atmospheric CO2 concentration increased plant water use efficiency, there was little change in basin-wide runoff because of the sparse vegetation cover. Neither did the 4C increase in air temperature much perturb total runoff. It did, however, cause seasonal snow melt to begin four to five weeks earlier than it currently does, allowing the melt water to infiltrate the soil more gradually and for a longer period of time than at present. The authors say this phenomenon is particularly beneficial, because the consequent gradual release of nitrates that are retained in the snowpack and otherwise released in a large pulse in the spring relieves some of the ecological pressure caused by high nitrate concentrations in typical springtime flows.

What it means
The results of this model study of ecosystem response to elevated air temperature and atmospheric CO2 enrichment in a high-elevation Rocky Mountain watershed are typical of what is found in nearly all ecosystems: improved water quality, enhanced plant water use efficiency, and higher levels of vegetative productivity, all of which consequences lead to greater plant populations and ecosystem biodiversity.


Reviewed 11 October 2000